Observations on the topography and the time sequences of calcium accumulation following single and repetitive cerebral ischemia, using 45-calcium radioautography, revealed significant differences in the pattern of calcium appearance between that seen in a single 5 minute bilateral carotid occlusion and that following three 90 second occlusions. Our observations indicate that accumulation of calcium during postischemic periods does not necessarily correlate with irreversible ischemic injury. Furthermore, our finding demonstrating that accumulation of calcium can take place in regions where the neurons were totally destroyed indicates that the uptake of calcium may include a significant component in non- neuronal elements. In view of the important role attributed to calcium in ischemic injury, further studies on mechanisms of calcium accumulation in ischemically affected brain tissue are under current investigation.